English grammer urgent

They (subject) are going on a picnic now.

The house was built by them(object).

^To leave( to+verb) To infinitive eg:-

I hate to leave home.
The plane leaves HK airport at 12:00.
My secretary has threatened to leave the office !
Bad students leave school at 15 .
To leave your wife dead after the murder.
She's leaving him for good.
not to be=not to leave--:-eg:-
to not do something or deal with something now:-
Leave the dishes (not to be cleaned now).
Why do you always leave everything until ordered to leave ?
Leave the door closed(=not open),please.
Don't leave her waiting when hurt !
She was to leave me with the impression that she was unhappy.
Is there anything left ?(= past tense of leave.)
What was left to me was what I need.
To leave from a place without taking her with you.
I've left my money on the bus.
Don't leave any of your belongings behind.
We had to leave the baby behind !
She left nothing to her son !
So I was left to cope on my own in life.
Someone left this banknote not for you ; not to be meant for you , but.....

Noun clause eg:-what I need.A noun cl.can be used as subject:-
eg:-What I need is an umbrella.
eg:-What I need surprised them.
As object:-
eg:-He gave me what I need.
eg:-He told her to buy what I need.
As object of preposition:-
eg:-It depends on what I need.
eg:-Don't ask on what I need.
eg:-Parents could not understand on what I need.
eg:-I agree about what I need.
eg:-Look at what I need.

What can be used as Subject or Object or Complement in a sentence?

- noun, pronoun, noun phrase
- infinitive phrase
- gerund phrase
- noun clause

2015-07-17 23:02:17 補充：
e.g. What I need is not to be a victim of your greed for power.

What I need - noun clause - subject
not to be a victim of your greed for power - infinitive phrase - subject complement

2015-07-17 23:05:09 補充：
e.g. To leave you makes me think of what I need.

To leave you - infinitive phrase - subject
what I need - noun clause - object of preposition "of"

They killed the boy. (They = subject)
The teacher punished them. (Them as a form of "they" = object)

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